Critical Patch Updates are collections of security fixes for Oracle products. CPU are released on the same date on java.com and Oracle Technology Network (OTN).

Limited Update

Limited Update (LU) dates reflect the release dates on OTN. LU releases on the java.com site are typically several days after OTN.

Patch Set Update

Patch Set Update (PSU) contain all of the security fixes in the CPUs released up to that version, as well as additional non-critical fixes. Java PSU releases should only be used if you are being impacted by one of the additional bugs fixed in that version. PSU dates reflect the release dates on OTN.

Security Alerts

Oracle will issue Security Alerts for vulnerability fixes deemed too critical to wait for distribution in the next Critical Patch Update. Alerts for the Java 7 release are listed here.
For more details see Oracle Critical Patch Updates and Security Alerts.